A surface pressure applying device for a slide gate described in JP 08-117985A and a surface pressure applying device for a slide valve described in JP 2003-200256A can be given as examples of this type of conventional surface pressure applying device for a slide valve.
A common slide valve device is placed at a bottom of a vessel for molten metal, and includes two or three plate bricks with an opening for controlling an outflow of the molten metal by sliding one of the plate bricks. While in use, the plate bricks receive pressure in proportion to the depth and density of the molten metal, but resist the pressure from the molten metal by keeping in close contact to each other utilizing the repulsive force of distorted springs. It is therefore common that the required spring force amounts to a few to ten-odd tons.
The structure disclosed in JP 08-117985A distorts the springs and thus applies pressure to the plate bricks by making a surface pressure bar and a roller engage with each other.
The structure disclosed in JP 2003-200256A relieves the surface pressure with a large-diameter roller which is attached to a surface pressure control bar and climbs over a mountain-like tapered portion formed on the top surface of a surface pressure releasing bar, thus depressing the surface pressure releasing bar and distorting the springs.
The structure of JP 08-117985A, the surface pressure bar and the roller are engaged with each other to distort the springs and apply pressure to the plate bricks, cannot avoid insufficient spring distortion which results from the friction between and deformation of the surface pressure bar and the roller. When the springs are not distorted enough, there is a possibility that the pressure applied to the plate bricks cannot withstand the pressure from the molten metal, thus inviting an accident in which the molten metal leaks.
In the structure of JP 2003-200256A, a large-diameter roller attached to a surface pressure control bar climbs over a mountain-like tapered portion formed on the top surface of a surface pressure releasing bar, thus depressing the surface pressure releasing bar, distorting the springs, and relieving the surface pressure, the tapered portion on the side on which the large-diameter roller climbs up needs to have as small an angle as possible to reduce the resistance met during the climb. The mountain-like tapered portion formed on the top surface of the surface pressure releasing bar is therefore given an asymmetric shape, making it difficult to match a spring arrangement center with the center between the peaks of two mountains. As a result, different loads are applied to two large-diameter rollers, and the one climbing over the mountain-like tapered portion that is nearer to the spring arrangement center receives an excessive load to be deformed and galled. The deformation and galling could prevent smooth movement.
The problem to be solved resides in that smooth movement of the plate bricks is hindered by the asymmetric shape of the mountain-like tapered portion of the surface pressure releasing bar which makes it difficult to match a spring arrangement center in the lateral direction with the arrangement center between the peaks of two mountains, or by insufficient distortion of the springs or the like.
The present invention is most characterized in that compression springs are distorted with an even force without allowing a shift of a surface pressure releasing bar to move engagement points with projections by making a spring arrangement center coincide completely with a projection arrangement center.
A surface pressure applying device for a slide valve according to the present invention makes a spring arrangement center coincide completely with an arrangement center around which projections formed on surface pressure releasing plates are arranged, and at the same time prevents a shift of a surface pressure releasing bar from moving engagement points with the projections. This enables the surface pressure applying device to distort the compression springs always with an even force, so that surface pressure is applied to and released from plate bricks steadily without fail.
In a case where the projections are constituted of rollers, the present invention makes the surface pressure releasing bar slide more smoothly.
The surface pressure releasing bar can slide smoothly also because an upper roller placed on a lower surface of a housing is in slidable contact with the surface pressure releasing bar.